There is known a detection device that detects a detection subject without contacting the detection subject.
The detection device, which is disclosed in the patent literature 1, includes a first coil and a second coil, which are placed on one side and the other side, respectively, of the magnet. A winding direction of the first coil and a winding direction of the second coil are opposite to each other. Furthermore, a wire, which forms the first coil, and a wire, which forms the second coil, are connected in series. Thereby, when a disturbance magnetic field is applied to the detection device, an electromotive force, which is generated in the first coil, and an electromotive force, which is generated in the second coil, are canceled with each other. Thereby, when the detection subject passes around the first coil, the detection device can detect an induced electromotive force, which is generated in the first coil, without being influenced by the disturbance magnetic fields.
However, in the patent literature 1, there is no disclosure with respect to a manufacturing method for winding the wire around a core. If the first coil and the second coil are separately formed and are thereafter joined together at a joint between the wire of the first coil and the wire of the second coil, these wires may possibly be broken at the joint at the time of applying a tension to the wires. Also, a manufacturing process of joining the wire of the first coil and the wire of the second coil together may possibly be complicated.